James Eagan Holmes is scheduled to be arraigned March 12 in the July 2012 Colorado theater shootings that killed 12 people.

By M. Alex Johnson, staff writer, NBC News

James Eagan Holmes, the man charged with killing 12 people and wounding 58 others in a crowded Colorado movie theater last year, may seek to plead not guilty by reason of insanity, his lawyers indicated in court documents made public Friday.

Holmes, 25, allegedly stormed a theater in Aurira, Colo., showing the premiere of "Batman: The Dark Knight Rises" on July 20 and opened fire with an armament of legally acquired weapons. He is charged with 166 counts of murder, attempted murder and other offenses.

Prosecutors still haven't said whether they intend to seek the death penalty for Holmes, who is scheduled to be arraigned March 12, and Friday's filing indicates that the lack of certainty is complicating his defense.

"Mr. Holmes is considering entering a plea pursuant to (the Colorado law governing insanity pleas), but he cannot intelligently decide how to proceed, until this Court rules upon certain legal issues related to the entry of such a plea and advises Mr. Holmes and counsel of the consequences of such a plea.

In five filings, Holmes' lawyers ask the court to declare parts of that law unconstitutional. Specifically, it argues that sections governing when a defendant may waive his right to remain silent and whether he must reveal confidential medical information are unconstitutionally vague.

Holmes' attorneys have previously said he suffers from mental illness, and he is known to have seen a psychiatrist at the University of Colorado Medical School before he dropped out a month before the shootings.

Only one person has been executed in Colorado since it legalized capital punishment in 1976.